Have you ever tried to install an extension or theme in Firefox and received the irritating “Invalid file hash (possible download corruption)” error message? Now you can work on resolving that problem with the following work-arounds.

The Infamous Message Window

This is probably the most irritating message window that is associated with installing extensions or themes in Firefox. For whatever reason, you start the installation and get this. Not good at all! So what do you do about it?

Possible Work-Arounds

Try the following methods to see if one will help get those problem extensions or themes installed.

Method 1 – Enable Third Party Cookies

Go to the Tools Menu and select Options.

Once the Options Window is open, choose the Privacy Tab

Select “Use custom settings for history” to in order to access the additional options

Make certain that “Accept third-party cookies” is selected

Click “OK”. (Restarting Firefox is recommended)

Method 2 – Manually Install The Extension

Right click on the extension or theme install link and select “Save Link As”

Once you have saved the extension or theme, drag the file into the Add-ons Manager Window with your mouse

Note: If for some reason manually installing the extension or theme still fails, there is a possibility that your anti-virus or another download monitoring software may be corrupting the file. In this case you could download the extension or theme on another computer and transfer it using a flash drive.

Method 3 – Clear The Cache

Go to the Tools Menu and select Options.

Once the Options Window is open, choose the Privacy Tab

Select “Use custom settings for history” to in order to access the additional options

Select “Clear history when Firefox closes” and then click on the “Settings Button”

Make certain that “Cache” is selected in the Settings Window (other options can all be deselected based on your needs)

Restart Firefox

Method 4 – Restart Firefox After “Failed Add-on Installation”

If you are installing directly from the Mozilla Add-ons website, there could be a problem with the Mozilla Add-ons website database or with a broken mirror website. Restart Firefox to see if the extension or theme did install regardless of the“Invalid file hash (possible download corruption)” error message.

Method 5 – Other Alternatives

Try installing the extension or theme again at a later time

Try installing the extension or theme from the add-on creator’s personal website

Hopefully with these tips you can bypass the error and enjoy more Firefox Add-on goodness.

Akemi IwayaAkemi Iwaya has been part of the How-To Geek team since 2009. She has previously written under the pen name "Asian Angel" and was a Lifehacker intern before joining How-To Geek. She has been quoted as an authoritative source by ZDNet Worldwide. Read Full Bio »